The present invention relates generally to a vehicle headlamp apparatus such as automobiles and more particularly to a vehicle headlamp apparatus having a light distribution control means or an AFS (Adaptive Front-Lighting System), for example, for making possible a follow-up change in the irradiating direction and irradiating range of a headlamp in response to the driving condition, wherein the optical axis of a headlamp is accurately set at a reference angle position, and to a method of setting the position of the optical axis of the vehicle headlamp apparatus.
The present applicant for patent has proposed the art of promoting car driving safety in the form of an AFS as mentioned in JP-A-2002-160581. As shown in the conceptual illustration of FIG. 1, the AFS employs a sensor 1 for detecting information indicating the driving conditions of a CAR in order to feed the detected output into an ECU (Electronic Control Unit) 2. The sensor 1 includes, for example, a steering sensor 1A for detecting the steering angle of the steering wheel SW of the CAR, a speed sensor 1B for detecting the speed of the CAR and a height sensor 1C for detecting the height of front and rear axles (only the rear axle is shown) in order to detect the leveling condition of the CAR, these sensors 1A, 1B and 1C being connected to the ECU 2. The ECU 2 operates to control a headlamp 3 whose light distribution characteristics are made variable by deflecting the directions of irradiation of swivel lamps 3R and 3L installed on the right and left sides of the front portion of the automobile on the basis of the output of the sensor 1 received. In such swivel lamps 3R and 3L, reflectors and projector lamps provided in the headlamp are allowed to swivel in the horizontal direction, for example, and a rotating drive means driven to rotate by a source of driving force such as a drive motor is installed. A mechanism including the rotating drive means is called an actuator hereinafter. With the AFS of this kind, it is possible to light the road ahead in proportion to the driving speed of the automobile when the automobile is driven on the curved road, which is effective in promoting driving safety.
In order to implement proper lighting, the steering angle of the steering wheel and the deflection angle of each swivel lamp should be set accurately; otherwise the optical axis of the swivel lamp may be turned to an undesirable direction with respect to the travel direction of the automobile, for example, the swivel lamp fails to light forward when the automobile is moving straight ahead or running on the curved road. Moreover, the swivel lamp may be deflected toward the oncoming lane and may blind oncoming traffic; the problem is that the driving safety is endangered.
Therefore, swivel lamp is initialized so as to direct the swivel lamp to a predetermined reference angle position, usually turning the swivel lamp to the direction in which the automobile is moving straight ahead in the conventional AFS when the ignition switch of the automobile is turned on. Thus the steering wheel SW can be matched off against the deflection angle of the swivel lamp and the proper deflecting operation becomes performable hereafter with the initialized reference angle position as a reference. However, the present deflected angle of the swivel lamp needs detecting for the initialization of the swivel lamp and in a conventional actuator of this sort, there is provided a deflection angle detector for detecting the deflected angle of the torque output shaft of the actuator correspondingly related to the deflected angle of the swivel lamp. For example, a potentiometer is attached to the output shaft of the rotating drive means for driving the swivel lamp to rotate so as to detect the angle of rotation, namely, the deflected angle, of the output shaft from the output of the potentiometer.
Notwithstanding, the setting of the potentiometer is undesirable mainly because the actuator tends to become complicated in structure and size. Hence, it has been considered to detect the deflected angle of the swivel lamp by detecting the angle of rotation of the drive motor as the drive source of the rotating drive means of the actuator and consequently Hall elements and Hall ICs (hereinafter called the Hall element) for outputting pulse signals corresponding to the number of revolutions of the drive motor as the rotating drive means. In other words, the deflected angle of the actuator is indirectly detected by counting the pulse signals issued from the Hall elements accompanied with the rotational operation of the drive motor, so that the proper control of the AFS is implemented.
Initialization to be carried out under a one-side contact system has been examined as a means for initializing swivel lamps by utilizing pulse signals from the Hall elements. The initialization by the one-side contact system is as shown in the conceptual illustration of FIG. 12B carried out by unidirectionally pivoting the swivel lamp, that is, a projector lamp 30 until the projector lamp is brought into contact with a stopper from a first position S, that is, up to the right-side maximum deflection angle position θr in this case. The projector lamp 30 is pivoted from the contact position θr in the opposite direction and simultaneously the counting of the pulse signals from the Hall element is started and is then stopped at a point of time the preset pulse signals are counted. Consequently, on condition that the counted number of pulse signals in relation with the deflected angle of the projector lamp 30 is gained beforehand, the projector lamp 30 can be pivoted from the contact position θr by a predetermined deflection angle θz, depending on the counted number of pulse signals, whereby the predetermined reference angle position of the projector lamp 30 can be set in the direction of going straight ahead in this case.
In carrying out the initialization under the one-side contact system, the position θr where the projector lamp 30 is brought into contact with the stopper in one direction is equivalent to a setting start angle position at the time of setting and pulse signals are counted from the setting start angle position by the deflection angle θz so as to set the reference angle position in the direction of going straight ahead. Consequently, a deflection θx is produced and when the setting start angle position falls on the position θr′, the deflection θx directly causes an error of the reference angle position to be produced. In other words, when the projector lamp 30 is brought into contact with the stopper in one direction, the deflection due to stress occurs in the projector lamp and the actuator and this results in turning the drive motor excessively by the angle θx because of the deflection, so that an error is produced in the setting start angle position. When the elastic modulus and thermal expansion coefficient of material such as resin and metal used for the projector lamp and the actuator are taken into consideration, the values of the elastic modulus and thermal expansion coefficient vary with the temperature and the deflection θx also varies with the temperature change, which causes an error in the setting start angle position as well. Therefore, an error is produced in the reference angle position when the projector lamp 30 is put back in the opposite direction by the predetermined deflection angle θz and this develops a problem arising from failing to secure the proper control of the AFS hereafter.